The programme brings together data from several long-running BTO schemes.

• Changes in numbers of breeding birds are measured by:
  • the BTO/JNCC/RSPB Breeding Bird Survey (BBS) – which began in 1994 and replaced the CBC (below) as the major monitoring scheme for landbirds, after a seven-year overlap. BBS is based on around 3000 1-km squares, within each of which birdwatchers count and record birds in a standardised manner along a 2-km transect. Because the survey squares are chosen randomly, the results are not biased towards particular habitats or regions. Combined CBC/BBS indices now provide long-running and ongoing population monitoring for many common birds.
  • the Common Birds Census (CBC) – which ran from 1962 to 2000. This scheme mapped the breeding territories of common birds on 200–300 mainly farmland and woodland plots each year, averaging about 70 and 20 ha respectively.
  • the Waterways Bird Survey (WBS) – which ran from 1974 to 2007. WBS observers mapped the territories of birds along rivers, streams and canals on 80–130 plots each year, each on average 4.5 km long. WBS has now been replaced by WBBS, a transect scheme akin to BBS but with transects running alongside linear waterways, which started in 1998.
  • the Constant Effort Sites Scheme (CES) – which began in 1983 and is based on bird ringing at over 100 sites. The catching effort is kept constant at each site during each year, so that changes in numbers of birds caught will reflect population changes and not variation in catching effort.
  • the Heronries Census – through which counts of 'apparently occupied nests' have been collected from a high proportion of the UK's heronries every year since 1928.
• Changes in breeding performance are measured by:
  • the Nest Record Scheme – which began in 1939 and collates standardised information on up to 35,000 individual nesting attempts per year. This allows the measurement of:
    • laying dates
    • clutch sizes
    • brood sizes
    • nesting success during egg and chick stages.
  • the CES (see above) – which provides information on overall productivity for a range of species by measuring the ratio of juveniles to adults caught each year.
• Changes in survival are measured by:
  • the British and Irish Ringing Scheme – which provides information on the finding circumstances and longevity of ringed birds found dead by members of the public.
  • The CES can also provide information on survival rates, based on the recapture of ringed birds at CES sites. In future further information on survival rates will be provided through the Retrapping Adults for Survival (RAS) scheme.

The ways in which the schemes fit together are shown in the diagram below, which also demonstrates the way in which the BTO aims to combine all this information to understand the mechanisms behind changes in population sizes using population models.

Next section –1.2 The value of combining results from different monitoring schemes

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